1. Field of the Invention
The present invention relates to a sensor device for detecting magnetic particles contained in a specimen or a target substance contained in a specimen with the magnetic particles as a label and a detection method.
2. Description of the Related Art
As a quantitative immunoassay, RIA or IRMA (radio immunoassay or immunoradiometric assay) have been known since a long time ago. According to this method, a competitive antigen or antibody is labeled by a radioactive nuclide, and from a measurement result of specific activity, the antigen is quantitatively measured. That is, the target substance such as the antigen is labeled, and is indirectly measured. Since this method has a high sensibility, it has greatly contributed to clinical diagnosis, but because of a problem of safety of radioactive nuclide, it has a weak side that requires a dedicated facility and apparatus. Hence, as a more workable method, for example, a method of using a label such as fluorescent material, enzyme, electrochemical emission molecule, and magnetic particles has been proposed. When a fluorescent label, enzyme label, electrochemical emission label, and the like are used as a label, they are used for an optical measuring method, and by measuring absorption coefficient and transmittivity of a light or an emitted light amount, the detection of the target substance is performed. EIA (Enzyme Immunoassay) using enzyme for a label is a method in which an antigen-antibody reaction is acted, and after that, an enzyme labeled antibody is reacted, and a substrate for the enzyme is added so as to cause color formation, and depending on its absorbance, colorimetry is carried out. Further, research papers on a biosensor for indirectly detecting biomolecule by a magnetic sensor element with the magnetic particles as a label have been issued by several research organizations.
The magnetic particles as a label need to be selectively immobilized on the target substance, and to obtain high detecting sensitivity and few variations in measurement value, it was necessary that a large number of labels are reacted enough time. Hence, when the magnetic particles are used for a label, as illustrated in FIG. 7, an idea is proposed, in which a wiring 420 for generating a magnetic field is disposed around a magnetic sensor 200, and by letting flow the current into this wiring 420, the magnetic field is generated to attract the magnetic particles, and contact probability with the magnetic particle and the target substance is increased so that the reaction is effectively carried out, thereby solving the above described problem. (Hugo A. Ferreira et al., IEEE Trans. Magn. 41, 4140 (2005) (hereinafter, referred to as Document 1)).
The technique disclosed in Document 1 is useful from the viewpoint of collecting the magnetic particles from a wider range. However, when attention is paid to a narrower range, it is recognized that the place in which the magnetic particles tend to come together is on the wiring to generate the magnetic field, and this is not enough for the purpose of collecting the magnetic particles on the sensor. Further, since a large magnetic field needs to be generated in order to collect the magnetic particles, there is a problem, for example, that it affects the magnetic sensor comprising a magnetic substance such as a magneto-resistive effect film.
A constitution as an improvement of the above wherein a magnetic particles collection efficiency was increased has been proposed in D. L. Graham et al., Sensors and Actuators B 107, 936 (2005). In the constitution, the magnetic particles is collected on a wiring provided in the vicinity of a giant magneto-resistance effect (GMR) sensor (the first process) and then an electric current was sent into wirings for detection connected to both ends of the GMR sensor and into the GMR sensor itself to collect the magnetic particles on the sensor (the second process). In the constitution, however, both the magnetic field caused by the GMR sensor and the magnetic field caused by the wirings connected to the both ends thereof introduce the same magnetic force at the magnetic particles collected in the first process. As a result, the magnetic particles are collected on not only the GMR sensor but also the wirings. The magnetic particles collected on the wirings do not contribute to the detection. The constitution is accordingly not preferable.